A method for measuring the coagulation of blood is known from German OS No. 24 06 484, wherein blood is adapted to be drawn from a storage vessel into a tube connected to a cylinder by means of a piston which is provided in the said cylinder and is moved therein in such a manner as to produce suction in the said tube. The piston is connected to a drive which then moves it back and forth in such a manner that the volume of blood drawn into the tube also carries out reciprocating movements in the tube. During these movements, the gas between the piston and the volume of blood is successively expanded and compressed. The change in the pressure of this gas is measured as an indication of the change in viscosity and coagulation of the blood.
With a method of this kind, one problem is that blood-coagulation cannot be measured under physiological conditions since the formation of a thrombus in the tube is influenced by the pressures acting upon it. In addition to this, the change in pressure arising in the gas, which is used in this method to measure coagulation, can be measured only relatively inaccurately and with difficulty. The pressure-measuring unit used in this connection, which consists of a U-shaped glass tube one end of which communicates with the gas-space between the piston and the volume of blood drawn in, is difficult to handle, since care must at all times be taken to ensure that the liquid in the U-shaped glass tube, for example mercury, does not escape therefrom, which might well happen if, as a result of inexpert manipulation, for example, the whole measuring unit were to be turned upside down. This may often happen during shipping and the mercury cannot therefore be placed in the apparatus by the manufacturer. This must be done when it has been set up at its destination, for example in a laboratory. The read-off from the scale fitted to the U-shaped glass tube is relatively time-consuming and inaccurate.
It is therefore the purpose of the present invention to provide a relatively accurate method for measuring the aggregation of blood-platelets or the coagulation of blood, which will allow the measurements to be made under physiological conditions, and an apparatus for the implementation of this method which is relatively simple to handle.
A more important advantage of the invention is that, for the first time, the aggregation of blood-platelets or the coagulation of blood can be measured under physiological conditions, i.e., with the blood under a predetermined, constant pressure. This makes it possible to imitate exactly the procedures taking place in the body, for example as a result of hemorrhage from a cut, or the like.
Another advantage of the invention is that more accurate, reproducible measurements can be taken.
It is also an advantage that the invention makes it possible to simulate cases in which the pressure acting upon the blood can be varied, over a predetermined period of time, in an accurately predetermined manner; for example, the pressure may increase and then decrease according to a predetermined, time-dependent function. Such pressure patterns (blood-pressure fluctuations) may also occur in the human body. It is thus possible, for the first time, to simulate specific disease symptoms by intentional, time-dependent changes in pressure.
Another advantage of the invention is that the design of the apparatus may be extremely functional, reliable, compact and simple.
The method and apparatus according to the invention are highly suitable for carrying out "on-line" measurements on patients who are in a critical phase, for example, after a kidney transplant or the like. At intervals of about 10 minutes, computer-controlled measurements may be carried out automatically. This makes it possible to determine the rate of change in platelet-aggregation and blood coagulation, this being an indication of morbid events, for example consumption-coagulopathy.